Searching for the Source of Carpal Lameness

The equine carpal (knee) joint is a veritable puzzle of bones and sometimes a diagnostic enigma for veterinarians. Mike Ross, DVM, Dipl. ACVS, of the University of Pennsylvania's New Bolton Center offered some insight to practitioners on working up horses with carpal pain at the Florida Association of Equine Practitioners (FAEP) Promoting Excellence Symposium, held Sept. 27-29, 2007, at the Atlantis resort on Paradise Island, the Bahamas.

Ross showed several case study videos to illustrate the telltale gait displayed by horses with problems in this region and explain his exam process.

"I think the carpal region may be about as good as it gets when it comes to looking at a horse and being able to say 'Yup, that's where the horse is lame,'" Ross said. He said that detecting heat in the area is a classic sign that remains accurate when considering knee pain as a diagnosis, and that looking for effusion (excess fluid) can also help guide a veterinarian. And when a horse with carpal joint pain moves, the lameness is often worse when the affected leg is to the inside of the circle. Horses with knee pain might also place their affected leg wide when trotting.

Beyond that, things can get a little tricky. Palpating the multifaceted but unyielding surface of the knee isn't likely to elucidate what's happening inside this complex structure.

"It is surprising to think how much disease can be there and how limited you are as far as your palpation options go," Ross noted.

It can also be difficult to perform diagnostic nerve blocks in this area. The carpal joint spaces run together, meaning that a high block administered early in the exam can travel down into other structures, potentially muddying up the waters for the veterinarian looking to pinpoint the cause of the horse's pain. Ross suggested starting blocks in this area in the distal aspect (bottom) and working upward.

Scintigraphy can highlight problem areas of bone remodeling and provide a guidepost for where to shoot the most telling radiographs in these cases. Ross also noted that searching for carpal pathology could be a valuable application for equine MRI technology in the future.

Some of the culprits behind pain in this region include chip fractures and sclerotic, remodeled bone.

And, of course, pinpointing the carpal pain might only be the beginning of the exam for the affected horse: "Compensatory lameness is a huge problem, I think," Ross said. "They get lame in one leg, overload another leg, and become lame in that one."